1. Field of the Invention
The present disclosure relates to a liquid crystal display device, and more particularly, to a bi-stable chiral splay nematic mode liquid crystal display device having a reflective type or a transflective type.
2. Discussion of the Related Art
As the information age progresses, display devices having superiorities of thin profile, light-weight and low power consumption have been required, and flat panel display (FPD) devices have been widely developed. Specifically, a liquid crystal display (LCD) device has been widely used for a notebook or a monitor of a desktop computer because of its superiorities in resolution, color displaying and display quality.
In general, the LCD device includes two facing substrates having their respective electrodes and a liquid crystal layer between the two substrates. An electric field is generated by applying voltages to the electrodes, and liquid crystal molecules in the liquid crystal layer are re-aligned by the electric field. As a result, transmittance of the liquid crystal layer is changed and the LCD device displays images.
FIG. 1 is an exploded perspective view showing a liquid crystal display device according to the related art. In FIG. 1, the liquid crystal display (LCD) device includes an array substrate 10, a color filter substrate 20 and a liquid crystal layer 30 between the array substrate 10 and the color filter substrate 20. The array substrate 10 includes a first substrate 12, a plurality of gate lines 14 on the first substrate 12, a plurality of data lines 16 crossing the plurality of gate lines 14 to define a pixel region P, a thin film transistor (TFT) Tr connected to the gate line 14 and the data line 16 and a pixel electrode 18 connected to the TFT Tr.
In addition, the color filter substrate 20 facing the array substrate 10 includes a second substrate 22, a black matrix 25 blocking a non-display area corresponding to the gate line 14, the data line 16 and the TFT Tr, a color filter layer 26 including red, green and blue color filters 26a, 26b and 26c each corresponding to the pixel region P and a common electrode 28 on an entire surface of the second substrate 22.
Although not shown in FIG. 1, a seal pattern may be formed in a boundary portion between the array substrate 10 and the color filter substrate 20 for preventing leakage of the liquid crystal layer 30. A lower orientation film may be formed between the array substrate 10 and the liquid crystal layer 30 and an upper orientation film may be formed between the color filter substrate 20 and the liquid crystal layer 30 for aligning the liquid crystal layer initially. Further, first and second polarizing plates may be formed on outer surfaces of the first and second substrates 12 and 22, respectively.
A backlight unit may be disposed under the array substrate 10 to supply light. When a gate signal turning on the TFT Tr is sequentially supplied the plurality of gate lines 14, the TFT Tr is turned on and a data signal supplied to the plurality of data lines 16 is applied to the pixel electrode 18 through the TFT Tr. As a result, a vertical electric field is generated between the pixel electrode 18 and the common electrode 28 and liquid crystal molecules in the liquid crystal layer 30 are re-aligned by the vertical electric field, thereby the LCD device displaying images due to transmittance change of the liquid crystal layer 30.
The liquid crystal layer 30 may have one of a nematic liquid crystal molecule, a smectic liquid crystal molecule and a cholesteric liquid crystal molecule. The nematic liquid crystal molecule having a strong scattering property in random alignment has been widely used for the LCD device. An electro optic effect of the liquid crystal means a change of optical properties due to an electric field. For example, an alignment of the liquid crystal molecules may be changed by an electric field. An alignment of the nematic liquid crystal molecules may be sequentially changed according to an electric field, and the LCD device including the nematic liquid crystal molecules may generally have a twisted nematic (TN) mode or a super twisted nematic (STN) mode.
In the TN mode LCD device, the liquid crystal molecules adjacent to the pixel electrode and the common electrode are initially oriented to be parallel to the pixel electrode and the common electrode, and a long axis of the liquid crystal molecule adjacent to the pixel electrode and a long axis of the liquid crystal molecule adjacent to the common electrode make a twist angle of about 90°.
In the STN mode LCD device, the liquid crystal molecules adjacent to the pixel electrode and the common electrode are initially oriented to be parallel to the pixel electrode and the common electrode, and a long axis of the liquid crystal molecule adjacent to the pixel electrode and a long axis of the liquid crystal molecule adjacent to the common electrode make a twist angle of about 180° or 360°.
Recently, the LCD devices of various modes have been suggested to satisfy various users' needs. Specifically, an E-book or an E-paper, where a fixed image such as a text or a photograph is displayed for a relatively long time period without changes, has been the subject of research and development. When the TN mode LCD device or the STN mode LCD device is applied to the E-book or the E-paper, a relatively high power is unnecessarily consumed for displaying a fixed image during a relatively long time period as for displaying a moving image. In addition, since the transmissive type LCD device requires a backlight unit, the E-book or the E-paper using the transmissive type LCD device has disadvantages in light-weight, thin profile and low power consumption. As a result, an LCD device applicable to an E-book or an E-paper with lower power consumption has been required.